Pressurized Vapor Cycle Liquid Distillation

ABSTRACT

Embodiments of the invention are directed toward a novel pressurized vapor cycle for distilling liquids. In some embodiments of the invention, a liquid purification system is revealed, including the elements of an input for receiving untreated liquid, a vaporizer coupled to the input for transforming the liquid to vapor, a head chamber for collecting the vapor, a vapor pump with an internal drive shaft and an eccentric rotor with a rotatable housing for compressing vapor, and a condenser in communication with the vapor pump for transforming the compressed vapor into a distilled product. Other embodiments of the invention are directed toward heat management, and other process enhancements for making the system especially efficient.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. application Ser. No.10/713,617 filed on Nov. 13, 2003, herein incorporated by referencewhich claims priority from U.S. Provisional Patent Application60/425,820, filed Nov. 13, 2002, U.S. Provisional Patent Application60/490, 615, filed Jul. 28, 2003, and the U.S. Provisional PatentApplication 60/518,782, filed Nov. 10, 2003, each of which is herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to liquid purification, and moreparticularly to liquid purification by vapor compression distillationcomprising a liquid ring pump with rotatable housing having an internalliquid recovery system.

BACKGROUND OF THE INVENTION

A dependable source of clean water eludes vast segments of humanity. Forexample, the Canadian International Development Agency reports thatabout 1.2 billion people lack access to safe drinking water. Publishedreports attribute millions and millions of deaths per year, mostlychildren, to water related diseases. Many water purification techniquesare well known, including carbon filters, chlorination, pasteurization,and reverse osmosis. Many of these techniques are significantly affectedby variations in the water quality and do not address a wide variety ofcommon contaminants, such as bacteria, viruses, organics, arsenic, lead,mercury, and pesticides that can be found in water supplies in thedeveloping world and elsewhere. Some of these systems require access toa supply of consumables, such as filters or chemicals. Moreover, some ofthese techniques are only well suited to centralized, large-scale watersystems that require both a significant infrastructure and highlytrained operators. The ability to produce reliable clean water withoutregard to the water source, on a smaller, decentralized scale, withoutthe need for consumables and constant maintenance is very desirable,particularly in the developing world.

The use of vapor compression distillation to purify water is well knownand can address many of these concerns. However, the poor financialresources, limited technical assets, and low population density thatdoes not make it feasible to build centralized, large-scale watersystems in much of the developing world, also limits the availability ofadequate, affordable, and reliable power to operate vapor compressiondistillation systems, as well as hindering the ability to properlymaintain such systems. In such circumstances, an improved vaporcompression distillation system and associated components that increasesefficiency and production capability, while decreasing the necessarypower budget for system operation and the amount of system maintenancerequired may provide a solution.

SUMMARY OF THE INVENTION

In a first embodiment of the invention there is provided a liquidpurification system is provided that advantageously may be compact,inexpensive, and easily maintained. One embodiment has a distillationdevice with a liquid ring pump and a fully rotatable housing with asingle continuous shaft about which the liquid ring pump, motor androtor rotates, and a second shaft supporting the rotatable housing, withan internal or external combustion engine, preferably having motor rotorand magnets hermetically sealed within the fluid pressure boundary ofthe distillation system.

Another alternative embodiment has a distillation device with a liquidring pump encased in a fully rotatable housing within the head vaporspace of a still. Systemic heat sources can be redirected through amulti-line heat exchanger to maximize energy efficiency during thevaporization step. Back-wash lines may be directed to the intake fromthe head chamber of the evaporator/condenser, to keep uniqueflip-filters in the intake from fouling and to add heat into the heatexchange network. Further, a method of eliminating mist may beincorporated in the liquid ring pump component to eliminate contaminatedliquid droplets entrained in the vapor and prevent them from beingcarried along to the condenser and thereby contaminating the purifiedproduct.

Another particular embodiment has a distillation device with a liquidring pump and a fully rotatable housing with a single continuous shaftabout which the liquid ring pump, motor and rotor rotates, and a secondshaft supporting the rotatably housing, with an internal or externalcombustion engine and siphon pump in a lower reservoir to siphon liquidinto the chamber of the liquid ring pump. The result is a highlyefficient, easily accessed and maintained, relatively simple andinexpensive system for purifying a liquid.

Yet another is a method for removing contaminants from water comprisingdriving an electric generator by means of a thermal cycle engine forgenerating electrical power capacity, the thermal cycle engine includinga burner for combusting a fuel, employing at least a portion of theelectrical power capacity of the electric generator for powering a waterpurification unit, supplying source water to an input of the waterpurification unit, conveying heat output of the thermal cycle engine forsupplying heat to the water purification unit to reduce the amount ofelectrical power required to purify the water. Further embodiments mayadditionally comprise one or all of transferring heat from an exhaustgas of the burner to source water, heating an enclosure surrounding thewater purification unit to reduce thermal loss, vaporizing untreatedwater, and condensing vaporized water into distilled water product.

Another embodiment employs a backpressure regulator comprising a hingedarm having a closed position and a movable stop shaped to cover a portconnected to a pressurized conduit, the stop being held by a retainerattached to the arm, and the stop being positioned adjacent to the portwhen the arm is in the closed position, wherein the arm is away from theclosed position when the pressure conduit exceeds a set point, and thearm is in the closed position when the pressure in the conduit is lessthan the set point.

Additional advantages and specific aspects of the system will be morereadily ascertained from the drawings and the accompanying detaileddescription of the preferred embodiments, below.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention will be more readily understoodby reference to the following detailed description, taken with referenceto the accompanying drawings, in which:

FIG. 1A is a conceptual flow diagram of a possible embodiment of theoverall system designed in accordance with the present invention.

FIG. 1B is a schematic block diagram of a power source for use with thesystem shown in FIG. 1A in accordance with an embodiment of theinvention.

FIG. 2 shows the component power unit and water purification unit inaccordance with a preferred embodiment of the present invention.

FIG. 3 is a schematic block diagram of an auxiliary power unit forproviding electrical power and heat for water purification in accordancewith the present invention.

FIG. 4 is a schematic overview of an integral power unit/waterpurification system in accordance with an embodiment of the presentinvention.

FIG. 5A is a cross-sectional and top view of a rotor and stator inaccordance with a particular embodiment showing the support structurefor the input, the vanes and chambers between the vanes, and therotating drive shaft.

FIG. 5B is a side top view of a rotor and stator corresponding to theembodiment shown in FIG. 5A, showing the support structures for theinput and output, the vanes, the eccentric configuration within thehousing unit, and the drive shaft.

FIG. 5C is a top view of a rotor and stator corresponding to theembodiment shown in FIGS. 5A and 5B, showing support structures forinput and output, the vanes, the eccentric configuration within thehousing unit, and the drive shaft.

FIG. 5D is a cross-sectional view of a rotor and stator corresponding tothe embodiment shown in FIGS. 5A, 5B, and 5C showing vanes, drive shaft,and bearings.

FIG. 6A is a schematic diagram of a liquid ring pump in accordance witha specific embodiment of the present invention.

FIG. 6B is a top view of a rotor in accordance with an embodiment of thepresent invention showing multiple vanes and chambers between the vanes,and intake and exit holes in each individual chamber.

FIG. 7A is further detail of a liquid ring pump in accordance with aspecific embodiment of the present invention showing the stationaryintake port and the rotating drive shaft, rotor and housing unit.

FIG. 7B is a view of a seal which may be present between the stationaryand rotor sections of a liquid ring pump in accordance with a specificembodiment of the present invention, separating the intake orifice fromthe exit orifice.

FIG. 8 is a cross-sectional view of a liquid ring pump according to anembodiment of the present invention, showing a capacitive sensor.

FIG. 9 is a cross-sectional view of a liquid ring pump according to anembodiment of the present invention showing the eccentric rotor, rotorvanes, drive shaft with bearings, the rotating housing unit for theliquid ring pump, the still housing, and the cyclone effect andresulting mist and water droplet elimination from the steam.

FIG. 10 is a cross-sectional view of a particular embodiment of a liquidring pump in accordance with the present invention, showing ahermetically sealed motor rotor and magnets that are housed within thepressure and fluid boundary of the system, the drive shaft, rotor, androtating housing wherein water droplets are spun off and recycled backto the base water level of the pump, and a siphon pump for drawing waterup into the main chamber of the pump from the lower reservoir.

FIG. 11 is a detailed view of the hermetically sealed motor rotor shownin FIG. 10.

FIG. 12A is a view of the external pump housing and motor housing for anembodiment in accordance with that of FIG. 10, showing steam input andoutput ports.

FIG. 12B is a cross-sectional view of FIG. 12A, showing the motor withinits housing, the motor shaft and rotor, and the lower reservoir.

FIG. 12C is another cross-sectional view of FIG. 12A through a differentplane, again showing the motor within its housing, the motor shaft androtor, and the fluid line connecting to the lower reservoir, wherein thesiphon pump is now visible.

FIG. 13 is a detailed cross-sectional view of the lower reservoir ofFIG. 12C showing more clearly the siphon pump, the surrounding bearings,and fluid line.

FIG. 14A is a schematic of an overall system in accordance with anembodiment of the invention, showing the intake passing through a pump,into a heat exchanger, continuing into the core of the still wherein aheater vaporizes the liquid into steam in the head section after whichthe steam flows to the compressor and into the condenser, after whichcondensed product can be recovered.

FIG. 14B is a detailed schematic of an evaporator head and blowdownlevel sensor housing, showing an external connecting valve betweensource and blowdown fluid lines.

FIG. 15 shows an alternative embodiment of an evaporator/condenserhaving elastomer tube and shell seals.

FIG. 16A is a cross-sectional view of the evaporator/condenser coresection of the still. Individual heating layers and ribs in accordancewith a particular embodiment are shown, with input and output manifoldsand bolts, for connecting and attaching to the fluid distributionmanifold.

FIG. 16B is a detail of a cross-section of an evaporator/condenser coresection in accordance with FIG. 16A, showing how the ribs effectivelypartition the steam/evaporation from the liquid/condensation layers.

FIG. 17A is a view of one face of the pump side of a fluid distributionmanifold.

FIG. 17B is a view of a second face of the pump side of a fluiddistribution manifold.

FIG. 17C is a view of one face of the evaporator/condenser side of afluid distribution manifold.

FIG. 17D is a view of a second face of the evaporator/condenser side ofa fluid distribution manifold.

FIG. 18A is a side view of a coupler in accordance with an embodiment ofthe present invention, for connecting various flow lines and componentsin the overall system.

FIG. 18B is a top view of a coupler as depicted in FIG. 12A.

FIG. 19A is a schematic diagram of a multi-line heat exchanger inaccordance with a specific embodiment of the present invention showingmultiple two-channel heat exchangers that are plumbed to produce amulti-line effect.

FIG. 19B is an alternative heat exchanger in accordance with aparticular embodiment of the present invention showing a singlethree-channel heat exchanger wherein heat from a product stream andblowdown stream exchange with a cold intake but not with each other.

FIG. 20 is a schematic overview of the system showing pressuremeasurement of the system using a cold sensor.

FIG. 21A shows a view of a flip-filter with the intake stream andblowdown stream flowing through filter units, each filter unit rotatingaround a pivot joint about a center axis.

FIG. 21B shows flip filter housings and an alternative embodiment of amulti-unit flip filter.

FIG. 22 shows a view of a manual switch for changing water flow throughindividual units of a flip-filter, enabling backwashing of the unitswithout having to physically flip the filters.

FIG. 23A is side view of a backpressure regulator in accord with anembodiment of the invention.

FIG. 23B is a diagonal view of the backpressure regulator shown in FIG.23A.

FIG. 24A is a side view of a backpressure regulator with a verticallypositioned port in accord with an embodiment of the invention.

FIG. 24B is a diagonal view of the backpressure regulator shown in FIG.24A.

FIG. 25 is a schematic of a backpressure regulator implemented into aprocess, consistent with an embodiment of the invention.

FIG. 26A is a diagonal view of a backpressure regulator in accord withan embodiment of the invention.

FIG. 26B shows a close-up view of section C of FIG. 26A, depicting anotch in the port of the backpressure regulator.

FIG. 27A is a cutaway side view of a backpressure regulator consistentwith an embodiment of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Definitions. As used in this description and the accompanying claims,the following terms shall have the meanings indicated, unless thecontext otherwise requires.

The term “purifying” as used herein, and in any appended claims, refersto substantially reducing the concentration of one or more contaminantsto less than or equal to specified levels or otherwise substantiallyaltering the concentration of one or more contaminants to within aspecified range.

The term “specified levels” as used herein refers to some desired levelof concentration, as established by a user for a particular application.One instance of a specified level may be limiting a contaminant level ina fluid to carry out an industrial or commercial process. An example iseliminating contaminant levels in solvents or reactants to a levelacceptable to enable an industrially significant yield in a chemicalreaction (e.g., polymerization). Another instance of a specified levelmay be a certain contaminant level in a fluid as set forth by agovernmental or intergovernmental agency for safety or health reasons.Examples might include the concentration of one or more contaminants inwater to be used for drinking or particular health or medicalapplications, the concentration levels being set forth by organizationssuch as the World Health Organization or the U.S. EnvironmentalProtection Agency.

A conceptual flow diagram of an overall system in accordance with onepossible embodiment of the present invention is shown in FIG. 1A, withliquid flow paths indicated by arrows. In an embodiment of this type,liquid flows through the system from an intake 00 into an exchanger 400wherein exchanger 400 receives heat from at least one of a plurality ofsources including a condenser 200, a head 300, and exhaust (not shown)from a power source such as an internal or external combustion engine.Liquid continues flowing past heat exchanger 400 into a sump 500 andinto a core 600 in thermal contact with condenser 200. In the core 600,the liquid is partially vaporized. From core 600, the vapor pathproceeds into head 300 in communication with a compressor 100, and fromthere into condenser 200. After vapor is condensed, liquid proceeds fromcondenser 200 through heat exchanger 400, and finally into an exhaustregion 700 and then out as final distilled product.

A power source 800 is used to power the overall system. Power source 800may be coupled to a motor 150 (not shown) that is used to drivecompressor 100, particularly when compressor 100 is a steam pump, suchas a liquid ring pump. The power source 800 may also be used to provideelectrical energy to the other elements of the system shown in FIG. 1A.Power source 800 may be, for example, an electrical outlet, a standardinternal combustion (IC) generator or an external combustion generator.An IC generator and an external combustion generator advantageouslyproduce both power and thermal energy as shown in FIG. 1B, where engine802 produces both mechanical and thermal energy. Engine 802 may beeither an internal combustion engine or an external combustion engine. Agenerator 804, such as a permanent magnet brushless motor, is coupled toa crankshaft of the engine 802 and converts the mechanical energyproduced by the engine 802 to electrical energy, such as power 806.Engine 802 also produces exhaust gases 808 and heat 810. The thermalenergy produced by the engine 802 in the form of exhaust gas 808 andheat 810 may advantageously be used to provide heat to the system.

Alternatively, heat from electrical power generator 800 may berecaptured by channeling the engine exhaust into the insulated cavitythat surrounds the still, which lies between external housing and theindividual still components. In such an embodiment, exhaust blows acrossa finned heat exchanger that heats source liquid as it enters evaporator600.

Returning to FIG. 1A, the power source 800 is preferably an externalcombustion generator such as a Stirling engine generator. A Stirlingengine produces a thermal energy output in the form of exhaust gases andradiative heat. The exhaust gases of a Stirling engine are relativelyhot, typically 100° C. to 300° C., and represent 10 to 20% of thethermal energy produced by the Stirling engine. The exhaust produced bythe Stirling engine is typically a clean exhaust, comprising mainly CO₂,N₂, and water. A cooler of the Stirling engine may be used to rejectheat produced by the engine to the environment around the engine. Use ofan external combustion engine, such as a Stirling cycle engine, toprovide mechanical power for conversion into electrical power by meansof a generator is described in detail in U.S. Pat. No. 6,536,207 (Kamenet al.), issued Mar. 25, 2003, and incorporated herein by reference. Foradditional information relating to preferred embodiments of a Stirlingcycle engine, see co-pending U.S. patent application Ser. No.09/517,245, filed Mar. 2, 2000, entitled “Stirling Engine Thermal SystemImprovements”, and co-pending U.S. patent application Ser. No.09/517,808, filed Mar. 2, 2000, entitled “Auxiliary Power Unit,” whichare herein incorporated by reference in their entirety.

Pre-treatment of the liquid to be distilled, preferably water, may beconducted, in which case pre-treatment may occur prior to or withinintake 00. Pre-treatment operations may include any or all ofgross-filtering; treatment with chemical additives such aspolyphosphates, polyacetates, organic acids, or polyaspartates; andelectrochemical treatment such as an oscillating magnetic field or anelectrical current; degassing; and UV treatment. Additives may be addedin liquid form to the incoming liquid stream using a continuous pumpingmechanism such as a roller pump or pulsatile pump, including a standarddiaphragm pump or piezoelectric diaphragm pump. Alternatively, theadditives may be added by a semi-continuous mechanism using, forexample, a syringe pump, which, would require a re-load cycle, or abatch pumping system, wherein a small volume of the additive would bepumped into a holding volume or reservoir external to the system thatuniformly mixes the additive with the liquid before the liquid flowsinto the system. It is also envisioned that the user could simply drop aprescribed volume of the additive into, for example, a bucket containingthe liquid to be purified. Liquid additive may be loaded as either alifetime quantity (i.e., no consumables for the life of the machine), oras a disposable amount requiring re-loading after consumption.

Additives could also be added in solid form, wherein such additivescould be embedded in a time-release matrix inserted into theflow-through channel of intake 00. In this particular embodiment,replacement additive would need to be inserted periodically by the user.In yet another embodiment, a powder form of an additive could be addedin a batch system wherein the powder is added, for example in tabletform, to an external reservoir containing water to be purified whereinthe additive is uniformly mixed, similar to the batch system for addingliquid additives described above.

Post-treatment of the distilled product, preferably water, may occur, inwhich case post-treatment may occur preferably within an external outputregion (not shown). Post-treatment operations may include tasteadditives such as sugar-based additives for sweetening, acids fortartness, and minerals. Other additives, including nutrients, vitamins,stabilized proteins such as creatinine, and fats, and sugars may also beadded. Such additives may be added either in liquid or solid form,whether as a time-release tablet through which the output liquid flows,or a powder added to an external reservoir such as through a batchsystem. Alternatively, the additive may be added to the output liquidvia an internal coating of a separate collection reservoir or container,for example, by leaching or dissolution on contact. In such embodiments,the ability to detect purified liquid with and without the additive ispreferred. Detection systems in accordance with embodiments of thepresent invention include pH analysis, conductivity and hardnessanalysis, or other standard electrical-based assays. Such detectionsystems allow for replacement of additives, as needed, by triggering asignal mechanism when the additive level/quantity is below a pre-setlevel, or is undetectable.

In another embodiment, liquid characteristics, such as for example waterhardness, is monitored in the output and may be coupled with anindicator mechanism which signals that appropriate additives should beadded.

In yet another embodiment, ozone is systemically generated using, forexample, electric current or discharge methods, and added to the outputproduct for improved taste. Alternatively, air pumped through a HEPAfilter may be bubbled through the output liquid to improve palatabilityof the final purified product.

It is envisioned that other embodiments may include means for detectingnucleic acids, antigens and bio-organisms such as bacteria. Examples ofsuch detection means include nanoscale chemistry and biochemistrymicro-arrays known in the field and currently commercially available.Such arrays may also be used to monitor the presence and/or absence ofnutrients and other additives in the purified product, as discussedabove

In another embodiment, UV treatment may be used post-purification, forexample in a storage barrel or other container, to aid in maintenance ofthe purified product.

In another particular embodiment, a Stirling engine generator whichproduces exhaust high in CO₂ content is used as the power source 800 topower the overall system. In such an embodiment, the exhaust from theStirling engine is funneled back to intake 00 and used to acidify thewater to be purified as one means of pre-treatment. The acidification ofthe incoming water supply would result from the forced dissolution ofthe CO₂ (under pressure) in the exhaust, and the acidification mayreduce any scaling, such as lime build-up, that occurs in the system.Alternatively, the CO₂ exhaust may be channeled into the purifiedproduct as a means for post-treatment acidification.

The system provided in accordance with embodiments of the presentinvention has two basic functional components that may be combinedwithin a single integral unit or may be capable of separate operationand coupled as described herein for the purpose of local waterpurification. FIG. 2 depicts an embodiment of the invention in which apower unit 2010 is coupled electrically, via cable 2014, to provideelectrical power to a vapor compression water distillation unit 2012,with exhaust gas from the power unit coupled to convey heat to the waterdistillation unit via an exhaust duct 2016.

Thermal cycle engines are limited, by second law of thermodynamics, to afractional efficiency, i.e., a Carnot efficiency of (T_(H)−T_(C))/T_(H),where T_(H) and T_(C) are the temperatures of the available heat sourceand ambient thermal background, respectively. During the compressionphase of a heat engine cycle, heat must be exhausted from the system ina manner not entirely reversible, thus there will always be a surfeit ofexhaust heat. More significantly, moreover, not all the heat providedduring the expansion phase of the heat engine cycle is coupled into theworking fluid. Here, too, exhaust heat is generated that may be usedadvantageously for other purposes. The total heat thermodynamicallyavailable (i.e., in gas hotter than the ambient environment) in theburner exhaust is typically on the order of 10% of the total inputpower. For a power unit delivering on the order of a kilowatt ofelectrical power, as much as 700 W of heat may be available in anexhaust stream of gas at temperatures in the vicinity of 200° C. Inaccordance with embodiments of the present invention, the exhaust heat,as well as the electrical power generated by an engine-poweredgenerator, are used in the purification of water for human consumption,thereby advantageously providing an integrated system to which only rawwater and a fuel need be provided.

Moreover, external combustion engines, such as Stirling cycle engines,are capable of providing high thermal efficiency and low emission ofpollutants, when such methods are employed as efficient pumping ofoxidant (typically, air, and, referred to herein and in any appendedclaims, without limitation, as “air”) through the burner to providecombustion, and the recovery of hot exhaust leaving the heater head. Inmany applications, air is pre-heated, prior to combustion, nearly to thetemperature of the heater head, so as to achieve the stated objectivesof thermal efficiency. However, the high temperature of preheated air,desirable for achieving high thermal efficiency, complicates achievinglow-emission goals by making it difficult to premix the fuel and air andby requiring large amounts of excess air in order to limit the flametemperature. Technology directed toward overcoming these difficulties inorder to achieve efficient and low-emission operation of thermal enginesis described, for example, in U.S. Pat. No. 6,062,023 (Kerwin, et al.)issued May 16, 2000, and incorporated herein by reference.

External combustion engines are, additionally, conducive to the use of awide variety of fuels, including those most available under particularlocal circumstances, however the teachings of the present descriptionare not limited to such engines, and internal combustion engines arealso within the scope of the present invention. Internal combustionengines, however, impose difficulties due to the typically pollutednature of the exhausted gases, and external combustion engines arepreferably employed.

An embodiment of a power unit 2010 is shown schematically in FIG. 3.Power unit 2010 includes an external combustion engine 2101 coupled to agenerator 2102. In a preferred embodiment, the external combustionengine 2101 is a Stirling cycle engine. The outputs of the Stirlingcycle engine 2101 during operation include both mechanical energy andresidual heat energy. Heat produced in the combustion of a fuel in aburner 2104 is applied as an input to the Stirling cycle engine 2101,and partially converted to mechanical energy. The unconverted heat orthermal energy accounts for 65 to 85% of the energy released in theburner 2104. This heat is available to provide heating to the localenvironment around the power unit 2110 in two forms: a smaller flow ofexhaust gas from the burner 2104 and a much larger flow of heat rejectedat the cooler 2103 of the Stirling engine. Power unit 2110 may also bereferred to as an auxiliary power unit (APU). The exhaust gases arerelatively hot, typically 100 to 300° C., and represent 10 to 20% of thethermal energy produced by the Stirling engine 2101. The cooler rejects80 to 90% of the thermal energy at 10 to 20° C. above the ambienttemperature. The heat is rejected to either a flow of water or, moretypically, to the air via a radiator 2107. Stirling cycle engine 2101 ispreferably of a size such that power unit 2010 is transportable.

As shown in FIG. 3, Stirling engine 2101 is powered directly by a heatsource such as burner 2104. Burner 2104 combusts a fuel to produce hotexhaust gases which are used to drive the Stirling engine 2101. A burnercontrol unit 2109 is coupled to the burner 2104 and a fuel canister2110. Burner control unit 2109 delivers a fuel from the fuel canister2110 to the burner 2104. The burner controller 2109 also delivers ameasured amount of air to the burner 2104 to advantageously ensuresubstantially complete combustion. The fuel combusted by burner 2104 ispreferably a clean burning and commercially available fuel such aspropane. A clean burning fuel is a fuel that does not contain largeamounts of contaminants, the most important being sulfur. Natural gas,ethane, propane, butane, ethanol, methanol and liquefied petroleum gas(“LPG”) are all clean burning fuels when the contaminants are limited toa few percent. One example of a commercially available propane fuel isHD-5, an industry grade defined by the Society of Automotive Engineersand available from Bernzomatic. In accordance with an embodiment of theinvention, and as discussed in more detail below, the Stirling engine2101 and burner 2104 provide substantially complete combustion in orderto provide high thermal efficiency as well as low emissions. Thecharacteristics of high efficiency and low emissions may advantageouslyallow use of power unit 2010 indoors.

Generator 2102 is coupled to a crankshaft (not shown) of Stirling engine2101. It should be understood to one of ordinary skill in the art thatthe term generator encompasses the class of electric machines such asgenerators wherein mechanical energy is converted to electrical energyor motors wherein electrical energy is converted to mechanical energy.The generator 2102 is preferably a permanent magnet brushless motor. Arechargeable battery 2113 provides starting power for the power unit2010 as well as direct current (“DC”) power to a DC power output 2112.In a further embodiment, APU 2010 also advantageously providesalternating current (“AC”) power to an AC power output 2114. An inverter2116 is coupled to the battery 2113 in order to convert the DC powerproduced by battery 2113 to AC power. In the embodiment shown in FIG. 3,the battery 2113, inverter 2116 and AC power output 2114 are disposedwithin an enclosure 2120.

Utilization of the exhaust gas generated in the operation of power unit2010 is now described with reference to the schematic depiction of anembodiment of the invention in FIG. 4. Burner exhaust is directedthrough a heat conduit 2016 into enclosure 2504 of water purificationunit designated generally by numeral 2012. Heat conduit 2016 ispreferably a hose that may be plastic or corrugated metal surrounded byinsulation, however all means of conveying exhaust heat from power unit2010 to water purification unit 2012 are within the scope of the presentinvention. The exhaust gas, designated by arrow 2502, blows acrossfinned heat exchanger 2506, thereby heating the source water stream 2508as it travels to still evaporator 2510. The hot gas 2512 that fills thevolume surrounded by insulated enclosure 2504 essentially removes allthermal loss from the still system since the gas temperature within theinsulated cavity is hotter than surface 2514 of the still itself. Thus,there is substantially no heat flow from the still to the ambientenvironment, and losses on the order of 75 W for a still of 10gallon/hour capacity are thereby recovered. A microswitch 2518 sensesthe connection of hose 2016 coupling hot exhaust to purification unit2012 so that operation of the unit may account for the influx of hotgas.

In accordance with alternate embodiments of the invention, adding heatto exhaust stream 2502 is within the scope of the invention, whetherthrough addition of a post-burner (not shown) or using electrical powerfor ohmic heating.

During initial startup of the system, power unit 2010 is activated,providing both electrical power and hot exhaust. Warm-up of waterpurification unit 2012 is significantly accelerated since finned heatexchanger 2506 is initially below the dew point of the moisture contentof the exhaust, since the exhaust contains water as a primary combustionproduct. All the heat of vaporization of this water content is availableto heat source water as the water condenses on the fins of the heatexchanger. The heat of vaporization supplements heating of the fins byconvection of hot gas within the still cavity. Heating of the fins byconvection continues even after the fins reach the dew point of theexhaust.

In accordance with other embodiments of the present invention, powerunit 2010 and water purification unit 2012 may be further integrated bystreaming water from the purification unit through the power unit forcooling purposes. The use of source water for cooling presents problemsdue to the untreated nature of the water. Whereas using the productwater requires an added complexity of the system to allow for cooling ofthe power unit before the purification unit has warmed up to fulloperating conditions.

Some specific embodiments of the present invention may improve upon thebasic design of the liquid ring pump, particularly with respect toincreasing overall energy efficiency by reducing frictional losses. Apreferred embodiment of the present invention having a fully rotatablehousing that provides maximum reduction in frictional loss yet maintainssimplicity of design and cost-effectiveness of production is shown inFIGS. 5A through 5D. As can be seen in FIG. 5A, stator 9 is stationaryrelative to rotor 8, and comprises an intake 7 and exit 6. Steam isdrawn in at pressure P₁ and passes into rotor chamber 3. Rotor 8 isoff-set from a central axis Z upon which the rotating housing and theliquid ring pump are centered. As rotor 8 turns about central shaft 14with rotor bearings 16, the effective volume of chamber 3 decreases.Steam is thereby compressed to pressure P₂ as it is carried along arotational path into exit 6, to be routed to a condenser 200.Preferably, a rotatable housing (not shown) rotates with the liquid ringin the liquid ring pump, to reduce energy loss due to friction.

Stator 9 has support structures 26 in the input and output regions, asseen in FIG. 5B and FIG. 5C. The individual vanes 17 of rotor 8 can beseen below the support structures 26 in the top view of stator 9 shownin FIGS. 5B and 5C, as well as the eccentric placement of rotor 8 aboutthe central axis. This particular embodiment of a liquid ring pump isboth axially fed and axially ported and may have a vertical, horizontal,or other orientation during operation. FIG. 5D shows yet another view ofthis embodiment.

Preferably, a liquid ring pump in accordance with the present inventionis designed to operate within a fairly narrow range of input and outputpressure, such that generally, the system operates in the range of from5 to 15 psig. System pressure may be regulated using check valves torelease steam from chamber 3 of FIG. 5A-D. Improved system performanceis preferably achieved by placing exit 6 of the exhaust port at aspecific angle of rotation about the rotor axis, wherein the specificangle corresponds to the pressure rise desired for still operation. Oneembodiment of a specific port opening angle to regulate system pressureis shown in FIG. 5B. Exit 6 is placed at approximately 90 degrees ofrotation about the rotor access, allowing steam from chamber 3 to vent.Placing exit 6 at a high angle of rotation about the stator axis wouldraise the system pressure and lower pump throughput, while placing exit6 at a lower angle of rotation about the stator axis would result inlower system pressure and increased pump throughput. Choosing theplacement of exit 6 to optimize system pressure can yield improved pumpefficiency. Further, the placement of exit 6 to maintain system pressurecan minimize system complexity by eliminating check valves at theexhaust ports to chamber 3, thereby providing a simpler, morecost-effective compressor.

An alternative embodiment for a liquid ring pump is shown in FIG. 6A asa schematic diagram. In FIG. 6A, compressor 100 is an example of apossible liquid ring pump with an outer rotatable housing 10 thatencloses a single two-channel stator/body 9, and a rotor 8, wherein theseal surface between the rotatable housing 10 and stationary stator/body9 is a cylinder. Two-channel stator/body 9 is kept stationary inreference to a chamber 12 of pump 100 as well as to rotor 8 androtatable housing 10, and comprises an intake 7 and an exit 6. Steam isdrawn in at pressure P₁ and passes through an intake orifice 5. When theintake orifice 5 lines up with an intake hole 4 in rotor 8 as the rotorspins around stationary stator 9, the steam passes through intake hole 4into a rotor chamber 3. Rotor 8 is offset from a central axis Z so that,as rotor 8 turns, the effective volume of rotor chamber 3 decreases. Inthis way, steam is compressed to pressure P₂ as it is carried along arotational path to an exit hole 2 in rotor 8. As rotor 8 turns, exithole 2 lines up with an exit orifice 1 of stationary exit 6, and thesteam at pressure P₂ passes through exit orifice 1 into exit 6 to berouted to a condenser 200. In such an embodiment, rotatable housing 10rotates with water 19 present in chamber 12 thereby reducing frictionalenergy losses due to windage. There may also be a small hole 11 presentin the housing 10 to permit water 19 to leave and/or enter chamber 12,thereby controlling the liquid level in the pump. In addition, rotor 8has multiple vanes 17 that are readily apparent when rotor 8 is viewedfrom above, as in FIG. 6B. Individual rotor chamber 3, and individualintake hole 4 and exit hole 2 for each rotor chamber 3, are also easilyseen in this view.

Another alternative embodiment of a liquid ring pump, wherein theinterface between rotatable housing 10 and stator 9 is conical ratherthan cylindrical, is seen in FIG. 7A. In this embodiment, a rotor driveshaft 14 has an end 15 situated upon a bearing 16 that allows rotatablerotor housing 10 to rotate with rotor 8. Intake 7 and exit 6, withcorresponding intake orifice 5 and exit orifice 1, are kept stationarywith respect to rotor 8 and rotor housing 10.

In addition, there may be either a conical or axial seal 13 presentbetween stationary sections 6 and 7 and rotor 8. In the conicalembodiment seen most clearly in FIG. 7B, seal 13 thereby separatesintake orifice 5 from exit orifice 1 of rotor 8 to prevent leaks. Theliquid ring pumps shown in FIGS. 6 and 7 are both axially fed andradially ported, in contrast with the preferred embodiment of a liquidring pump, discussed with reference to FIGS. 5A-5D (vide supra), whichis axially fed and axially ported.

During operation, it may be desirable to measure the depth of the liquidring in the compressor, to optimize performance. In the embodimentsherein disclosed, liquid ring pump housing 10 rotates with the liquidring in the pump, and the temperature of the liquid is typically around110° C. Methods of measuring ring depth include any one of the usualmethods, such as using ultra-sound, radar, floats, fluid conductivity,and optical sensors. Because of the complexities of the rotatinghousing, use of a capacitive sensor is a preferred embodiment for thismeasurement, wherein as the depth of the liquid in the capacitorchanges, the capacitance of the capacitor also changes. As shown in FIG.8, a disc-shaped capacitor sensor plate 110 is mounted to the bottom ofrotating housing 10, equidistant from the bottom surface 10A of rotatinghousing 10, and the bottom surface 8A of rotor 8. The capacitor is thusdefined by housing 10, rotor 8, and capacitor sensor 110. Leads 112connect the capacitor, from capacitor sensor 110, through a passageway53A in rotating housing shaft 53, to the secondary 113 of a coretransformer, preferably of ferrite (not shown). In one embodiment, thesecondary 113 is rotating at the same speed as the capacitor plate, andis in inductive communication with the primary of the ferrite coretransformer. The primary winding 114 is stationary, and signals to andfrom the level-measuring capacitor are communicated through thetransformer, in this way enabling depth information to be transmittedfrom a rotating position to a stationary position. Capacitance ismeasure by determining the LC resonance of the capacitor (C) with theinductance (L) of the transformer secondary. In a preferred embodiment,an LC oscillator circuit is constructed and the oscillation frequency isused as a measure of the capacitance.

Alternatively, in another particular embodiment in accordance with theinvention, it can be envisioned that a regenerative blower might be usedin place of a liquid ring pump for compressor 100. An example of apossible regenerative blower that could be used instead of a liquid ringpump is the commercially available REGENAIR® R4 Series by GAST (e.g.models R4110-2/R4310A-2 et seq.), capable of operating at 52″ H₂Omaximum pressure, 92 cfm open flow, or 48″ H₂O maximum pressure, 88 cfnopen flow, respectively. See Appendix A, incorporated by referenceherein.

To prevent contaminated liquid droplets from being entrained and carriedalong with vapor to condenser 200, pump 100 may be designed as shown inthe alternative embodiment of FIG. 9, for example. In such anembodiment, the liquid ring pump is within the head space of theevaporator/condenser, and mist is eliminated as rotating housing 10rotates, wherein the rotation creates a cyclone effect, flinging mistand water droplets off by centrifugal force to collide with the stillhousing and run down to the water in the sump. There may also be fins 18extending from the outside of rotating housing 10 to enhance circulationand rotation of vapor in the annular space between rotating housing 10and fixed housing 25. A steam exit 22 is provided for passage of steamto condenser 200.

In a preferred embodiment, there may also be an actuator 150, such as amotor, for driving compressor/pump 100, as shown in FIG. 10. Motor 150receives power from power source 800 (shown in FIG. 1A). In theparticular embodiment shown in FIGS. 10 and 11, the motor rotor/magnets37 are hermetically sealed inside the pressure and fluid boundary of thesystem, and the motor can 27 and motor stator/windings 38 are locatedoutside the main pressure system envelope. A single continuous shaft 14spans the length from motor 150 to pump 100, about which sit bearings16, to enable rotation of motor rotor 37 and pump rotor 8. Use of ahermetically sealed motor and continuous shaft eliminates the need for asealed shaft penetration of the pressure boundary. In addition, themotor is maintained at a constant temperature by the surroundingsaturated steam and circulation of liquid intake 39 about motor stator38 (see FIG. 14A, infra). Heat generated by the motor is thereforetransferred into the system, reducing the overall heat input required tomaintain the temperature.

In one embodiment, motor 150 is a motor of the type designed to be runin steam and water, eliminating the need for shaft couplings andmechanical seals, thereby reducing drag and complexity in the mechanicalcomponents, and simultaneously allowing better recovery of motor powerloss. In such an embodiment, motor rotor 37 (see FIG. 10) is made oflaminations. To protect against rust, the laminations may be made ofsteel, and are protected by plasma coatings, silicone coatings, powdercoatings or the laminations and magnets may be plated with nickel.

In a more preferred embodiment, motor rotor 37 is a solid material rotorsuch as pure iron or stainless steel, for example, a high-chromiumcontent steel such as 446 stainless steel. The iron or steel rotors 37may be nickel-plated, as may be magnets 37A. Pure iron rotors have thebest magnetic properties, and improved torque relative to laminatedrotors. Alternatively, solid stainless steel rotors with nickel-platedmagnets may be used. Preferably the stainless steel has a high chromiumcontent, thereby creating a coating of chrome oxide on the surface ofrotor 37, which protects the iron content in the rotor from rust. Aswith pure iron rotors, stainless steel rotors also have improved torqueover laminated rotors.

In yet another embodiment, the high-chromium content stainless steelrotor may be passivated to remove surface iron, creating a thickchromium oxide coating for enhanced corrosion protection. Other appliedcoatings may be used to aid in corrosion resistance. In addition, thenickel-plated magnets may be curved surface magnets, which will furtherincrease motor torque and reduce manufacturing costs.

As shown in FIG. 10, motor housing 27 contains motor 150 with motorstator/windings 38. Motor can 28 hermetically seals motor rotor 37,motor magnets 37A, and motor and pump rotor continuous drive shaft 14within the fluid/pressure envelope of the system. Fixed housing 25encloses non-rotating valve-plate 33, and pump rotor 8 having multiplerotor vanes 17, rotor bearings 16, and a liquid ring 19 (see FIG. 6A or9), typically water, that rotates with rotating housing 10. A drain (notshown) on outer housing 25 prevents over filling of the liquid ring pumpstationary housing.

A lower reservoir 30 containing a level of liquid, connects to adrain/fill fluid line (not shown), and houses siphon pump 32 androtating housing bearings 52 about rotating housing shaft 53. Siphonpump 32 redirects liquid, preferably water, from lower reservoir 31 upsiphon pump line 35 and continuing through siphon feed line 36 intochamber 12. As rotor 8 and liquid ring 19 rotate, water droplets 20 areflung by centrifugal force outwards, through a liquid ring overflowopening (not shown), against fixed housing 25, and then run down fixedhousing wall 25 and back into lower reservoir 30.

FIG. 12A shows an embodiment in accordance with the present invention ofexternal fixed housing 25, external motor housing 27, exhaust and intakemanifolds 6 and 7, respectively, and motor can 28. FIG. 12B is across-sectional view of the embodiment depicted in FIG. 12A. Externalmotor housing 27, external housing 25, and lower reservoir 30, arevisible, including rotating housing bearings 52. In addition, a motorwith motor rotor 37, motor stator 38, and single continuous rotor shaft14 and rotor vanes 17 are also visible.

Similarly, FIG. 12C shows a cross-sectional view of the same embodimentas seen in FIGS. 12A and 12B, but through a different plane. Now, siphonpump 32, with siphon pump line 35 and siphon feed line 36 connectinginto chamber 12, can be readily seen within lower reservoir 30.

A detailed view of siphon pump 32 can be seen in FIG. 13, across-sectional view of lower reservoir 30. FIG. 13 shows lowerreservoir 30, within which can be seen rotating housing bearings 52 anda cut-away view of siphon pump 32, siphon pump line 35, siphon feed line36 and chamber 12. In operation, siphon pump 32 draws water from lowerreservoir 30, pumps the water up through siphon pump line 35 to siphonfeed line 36, and thereby back into chamber 12. With reference to FIG.10, embodiments of the invention that transfer fluid from lowerreservoir 30 to chamber 12 may utilize one or more baffles in lowerreservoir 30, preferably attached to the stationary, exterior housing25. The baffles, which preferably may be radial in configuration,disrupt the flow of fluid induced by the rotation of housing 10, toprevent loss of siphon in siphon pump 32, thereby maintaining bettersiphon flow and enabling prime if siphon is lost.

Another specific embodiment of the present invention is designed toimprove overall energy efficiency of the system, and is shown in FIG.14A. A system in accordance with this particular embodiment has coldliquid intake 39 flowing through pump intake 00, continuing throughexchanger 400. Pump 00 is typically a diaphragm positive-displacementpump, which is self-priming when the system is not pressurized—i.e., Pinside the system equals P outside. In a preferred embodiment, pump 00may also have a loop feedback configuration, with air vent 01, to helpprime pump 00 upon start-up, or more particularly, to re-prime theoperating system, under pressure, if the prime is lost, as would happenif the source hose were removed from the liquid source container.

From exchanger 400, the intake line may continue in a cooling loop aboutmotor 150, and then continue into core evaporator/condenser 600 whereincondenser 200 has a top core plate 48 and a bottom core plate 50. Withincore evaporator/condenser 600 may be multiple parallel tubes 49,typically made of copper-nickel alloy or other heat-transferablematerial, having head manifold openings 56 to allow core tubes 49 tocommunicate with head 300, and having sump manifold openings 55 to allowtubes 49 to communicate with sump 500. Core tubes 49 are the heatexchange surface through which the latent heat of evaporation istransferred in the evaporation/condensation cycle. The rate at whichheat can be exchanged between the condensing steam, outside the tubes,and evaporating water, inside the tubes, is a key factor in output rateand efficiency. If the thermal resistance of the heat exchange surfaceis low, better heat exchange occurs and output volume and efficiencyincreases. Any air impinged against the condensing surface becomes aninsulator that inhibits transfer of heat. To prevent this, any airpresent in the system is continuously vented out of the system, via, forexample, air vent 01, volatile mixer 23, or other venting outlets asrequired.

Heat transfer may also be adversely affected when water forms sheets asit condenses and coats the exterior of the tubes as it runs down to thebottom of the condenser chamber, a phenomenon known as “skinning.” Theextent to which the water “skins” on the surface of the condenser isdetermined largely by the surface energy (hydrophobicity) of the heattransfer surface. In an embodiment of the present invention, hydrophobiccoatings may be applied to cause condensing water to bead-up rather thanskin, thereby leaving more of the heat transfer surface exposed forefficient heat transfer. Examples of suitable hydrophobic coatingsinclude a coating manufactured by Ocular Technologies, or any otherhydrophobic coating that imposes little to no thermal resistance itself.

Steam 21 from the condenser section 600C of evaporator/condenser 600 mayalso feed into a volatile mixer 23 where volatile gases may be releasedfrom the system.

The system maintains a constant blowdown water flow to prevent scalingand other accumulation in the system. Water level 19 in head chamber 300is adjusted through a feedback control loop using level sensor L1, valveV1, and source pump 00, to maintain proper water flow through theblowdown stream 43. The three-way source pump fill valve 29 is set topump water into sump 500, which causes water level 19 in head chamber300 to rise. As liquid level 19 rises in head chamber 300, liquidoverflows past a dam-like barrier 302 into blowdown control chamber 301containing blowdown level sensor L1. As required, blowdown valve V1 iscontrolled to allow water flow from blowdown control chamber 301 throughheat exchanger 400, to extract heat and cool blowdown stream 43, andflow out valve V1, through volatile mixer 23 allowing cooling of hotgases and steam 21 from the evaporator section 600B, and then completingthe blowdown stream, out to waste 43A.

The system also maintains proper product flow. Product level 502 buildsup in condenser chamber 600C, and enters into product control chamber501, where product level sensor L2 is housed. Using a feedback controlloop with level sensor L2 and valve V2, product stream 41 is controlledto flow from product control chamber 501 through heat exchanger 400, toextract heat and cool product stream 41, then through valve V2 and onout to complete the product stream as product water outlet 41A.

The system may preferably be configured to maintain proper liquid ringpump water level by the use of a liquid recovery system to replenishliquid loss. There are several ways that liquid from the ring pump maybe depleted during system operation, including leakage into lowerreservoir 30, expulsion through exhaust port 6, and evaporation. Theleakage and expulsion losses can be large depending on operationalparameters, such as the speed of rotation and liquid ring pumpthroughput. These leakage and expulsion losses could require totalreplacement of the fluid in the pump several times per hour. Theevaporation loss is typically small.

Liquid level in the ring pump can be maintained by adding additionalsource water, product water, or preferably by re-circulating liquidwater lost from the liquid ring pump for improved system efficiency. Inone preferred embodiment, the liquid level in the ring pump is primarilymaintained by re-circulation of the liquid accumulated in lowerreservoir 30 in FIG. 14A. Liquid can accumulate in lower reservoir 30from leakage from the liquid ring pump and from fluid expelled inexhaust 57, captured in mist eliminator 58 and pumped to lower reservoir30. Alternatively, fluid expelled in exhaust 57 and captured in misteliminator 58 can be returned via the liquid ring pump exhaust port.Fluid accumulated in lower reservoir 30 can be re-circulated by one ofseveral pumping mechanisms. One preferred method is to use a siphon pump32 (described above) as shown in FIGS. 10 and 12C.

A minimum depth of water is preferably maintained in the lower reservoirfor the siphon pump 32 to perform properly. In one preferred embodiment,liquid ring pump control chamber 101, which houses liquid ring pumplevel sensor L3 can be used to control the liquid ring pump level andcontrol the level of water in the lower reservoir 30, as shown in FIG.14A. Liquid ring pump control chamber 101 is fluidly connected to liquidring pump 100 and lower reservoir 30. Liquid ring pump 100 is connectedto the three-way source fill valve 29, which is set to open when theliquid ring pump requires more water and it is also connected to theliquid ring pump drain valve V3, which opens when it is required todrain water from liquid ring pump 100 into blowdown stream 43.

If re-circulated water from lower reservoir 30 is not primarily used tomaintain the fluid level in the liquid ring pump, then either coldsource water or product water could to be used. In the event sourcewater were used, the introduction of cold water (which could beapproximately 85 degrees C. colder than system temperature) to theliquid ring pump would decrease system efficiency or alternatively theuse of a pre-heater for such cold source water would increase the energybudget of the system. Alternatively, the use of product water, while notadversely affecting system temperature, could decrease production leveland, thus, also lead to system inefficiency. At startup, the initialfluid level for the liquid ring pump is preferably supplied from sourcewater.

In one embodiment, the start-up time may be reduced by using an externalconnecting valve 43AA between source 39 and blowdown 43 fluid lines,located adjacent to heat exchanger 400, on the cold side, as shown inFIG. 14B. To determine the level of fluid in evaporator head 300 duringthe initial fill, connecting valve 43 would be open, blowdown valve BVwould be closed, and fluid would be pumped into the system throughsource line 39. Connecting blowdown 43 and source 39 lines results inequal fluid height in the blowdown level sensor housing 301 andevaporator head 300, thereby permitting a determination of fluid levelin evaporator head 300 and enabling the evaporator to be filled to theminimum required level at startup. Using the minimum level requiredshortens initial warm-up time and prevents spill-over from theevaporator head 300 through the liquid ring pump 100 to the condenser600 when the liquid ring pump 100 starts (see FIG. 14A).

The concentration of solids in blowdown stream 43 may be monitored andcontrolled to prevent precipitation of materials from solution and thusclogging of the system. Also during start-up, circulating pump 43BB cancirculate water through heat exchanger 400 to pre-heat the heatexchanger to the proper temperature for normal operation. A conductivitysensor (not shown) may be used to determine total dissolved solid (TDS)content by measuring the electrical conductivity of the fluid. In aparticular embodiment, the sensor is an inductive sensor, whereby noelectrically conductive material is in contact with the fluid stream. Ifthe TDS content in blowdown stream 43 rises above a prescribed level,for example, during distillation of sea water, the fluid source feedrate is increased. Increasing the fluid source feed rate will increasethe rate of blowdown stream 43, because distilled water productionchanges only slightly as a function of fluid feed rate, and an increasedblowdown stream rate results in reduced concentration of TDS, therebymaintaining overall efficiency and productivity of the system.

As discussed in relationship to FIG. 14A, fluid control is achieved byusing level sensors and variable flow valves in a feedbackconfiguration. Optimal operation of the still requires total fluid flowin to closely match total fluid flow out. Maintaining fluid levels inthe still at near constant levels accomplishes this requirement. In aparticular embodiment, the sensors are capacitive level sensors, aparticularly robust sensor for measuring fluid levels. Capacitive levelsensors have no moving parts and are insensitive to fouling, andmanufacture is simple and inexpensive. Opening of a variable flow valveis controlled by the level of liquid measured by the capacitive levelsensor, whereby the fluid level is adjusted at the level sensorlocation. A rising fluid level causes the valve to open more, increasingflow out of the sensor volume. Conversely, a falling fluid level causesthe valve to close more, decreasing flow out of the sensor volume.

Flow rate through the variable flow control valves and from the inputpump can be determined using an in-situ calibration technique. The levelsensors and associated level sensor volume can be used to determine thefill or empty rate of the sensor volume. By appropriately configuringthe control valves, the flow rate calibration of each valve and also ofthe source pump can be determined.

In a particular embodiment of the invention, a valve block (not shown)may be utilized to consolidate all control valves for the system into asingle part, which may be integrated with the fluid flow manifold. Acontrol system comprising a sensor for total dissolved solids andblowdown stream may also be incorporated, as well as a float valve orother device for controlling the height/level of liquid in the head.

As shown in FIG. 14A, there is additionally a steam flow line 22 fromhead 300 to compressor 100, a steam outlet 57 for diverting steam tocondenser 200, a hot product line 41 from condenser 200 leading throughexchanger 400, which also allows for collection of hot purifiedcondensed product 502, and a line (not shown) for diverting hot productto compressor 100 to allow adjustment of water level to keep itconstant. There may also be a drain line (not shown), for when thesystem is shut down.

Further, there may be a heater 900 with heating element 60 for heatingcold liquid to boiling at start-up, and for maintaining sufficient heatduring operation of the still to continuously convert liquid to steam.In one embodiment of the invention, the distillation system may operateat steady-state without thermal input from the heater 900 after systemstart up. Alternatively, a second heater (not shown) may be used tomaintain sufficient heat during operation; the heater may runcontinuously, in a pulsed mode, or be controlled by a controller.

In one particular embodiment, evaporator/condenser 600 isevaporator/condenser 600A having elastomer tube and shell seals 54A and54B for core tubes 49, as shown in FIG. 15, replacing end plates 48 and50, respectively, of FIG. 14A. Such elastomer tube and shell seals areexemplified in U.S. Pat. No. 4,520,868, which is hereby incorporated byreference herein. Tool-less clamp-on seals 59 external toevaporator/condenser 600A allow easy access for cleaning and repair, andreplacement of core tubes 49, if needed. Externally removable fittings47 may be used to couple fluid condenser steam inlet port 70, liquidproduct outlet port 66, evaporator steam outlet port 69, blowdown streamoutlet port 65, liquid input port 64, and volatile port 67 toevaporator/condenser 600A. In this particular embodiment, a thick filmheater 900A may be used to heat liquid in the sump, replacing heater 900and heating element 60 (see FIG. 14A).

In yet another particular embodiment in accordance with the inventionthere may be an evaporator/condenser 650, as shown in FIGS. 16A and 16B,in place of core 600. As seen in FIG. 16A, evaporator/condenser 650 is aflat evaporator/condenser and contains multiple parallel core layers 92and 94, typically made of copper-nickel alloy or other heat-transferablematerial, with rib sections 90 creating channels 95 and 97 for directingsteam and condensed liquid flow. Steam intake 7A and product exit 6Amanifolds (as well as dirty intake and volatile exit manifolds, notshown) connect via a fluid interface to liquid ring pump/compressor 100.Bolts 88 secure core evaporator/condenser 650 to brackets of externalhousing 25. In operation, every alternating horizontal (as shown inFIGS. 16A and 16B) row 92 and 94 comprises evaporator channels 95 andcondenser channels 97, such that the two functions never overlap on anygiven layer. FIG. 16B, a detail of FIG. 16A, shows more clearly how thecombined condenser/evaporator manifolding works. As indicated, rows 92do not interact with rows 94, they are closed off to each other, therebyseparating the functions of evaporation and condensation in thehorizontal core layers.

In addition, another particular embodiment in accordance with theinvention may include fluid distribution manifold 675, shown in FIGS.17A through 17D. FIG. 17A shows one face of the pump side of oneparticular embodiment of a fluid distribution manifold 675. Input, inthe form of raw source feed, flows through port 64, and blowdown stream(output) flows through port 65. Additional output in the form of productflows through port 66, while port/chamber 67 provides the vent forvolatiles (output) and port 68 provides the drain (output) for liquidring pump. FIG. 17B shows the other face of the pump side of the sameparticular embodiment of fluid distribution manifold 675. Port/chamber67, for output of volatiles, is apparent, as is the drain 68 for aliquid ring pump. In this view of this particular embodiment, acondenser steam mist eliminator chamber 71 is visible, as is a mistcollector and drain area 73.

FIG. 17C shows one face of the evaporator/condenser side of the sameparticular embodiment of fluid distribution manifold 675. Raw sourcefeed port 64, as well as blowdown passage ports 65 and product passageports 66, are readily visible in this view. In addition, evaporatorsteam passage port 69 and condenser steam passage port 70 can be seen.

Finally, FIG. 17D shows the other face of the evaporator/condenser sideof the same particular embodiment of fluid distribution manifold 675.Again blowdown passage port 65 is visible, as is liquid ring pump drainport 68, a second condenser steam mist eliminator 71, evaporator steammist eliminator 72, and mist collector and drain area 73. Also, a sumplevel control chamber can be seen in this view, along with a productlevel control chamber 75 and a liquid ring pump supply feed 76.

In such a particular embodiment, a fluid distribution manifold 675 iscapable of eliminating most plumbing in a liquid purification system,advantageously incorporating various functionality in one unit,including flow regulation, mist removal, and pressure regulation,thereby simplifying manufacture and significantly reducing overallcomponent parts. The core plates and manifolding may be made of, forexample, plastic, metal, or ceramic plates, or any other non-corrosivematerial capable of withstanding high temperature and pressure. Methodsof manufacture for the core plates and manifolding include brazing andover-molding.

FIGS. 18A and 18B show couplers that allow fluid interfacing throughoutthe system in a particular embodiment. For example, there may be afloating fluid interface between exchanger 400 and intake/exhaust ports7 and 6 seen in FIG. 12A. FIG. 18A shows such a fitting 61 that can bewelded to heat exchanger ports (not shown), wherein fitting 61 connectsto fluid interface 62 which is in turn in communication with the fluiddistribution manifold. FIG. 18A shows a sectional view across line A-A(see FIG. 18B). Fitting 61 has the ability to float to compensate forshifts in registration, possibly caused by temperature or manufacturingvariations. Sealing is accomplished by o-ring 63. As can be seen in theview depicted in FIG. 18B, o-ring seal 63, upon rotation of line A-A 90°about a central axis, fitting 61 and fluid interface 62 lock together tomake a fluid interface connection.

For either core 600 having core tubes 49, or core 650 having parallelcore layers 92 and 94, the geometry of the core tubing or layer channelsmay be cylindrical, square, rectangular, and the like. In still anotherspecific embodiment in accordance with the present invention, coreconfigurations may be selected to increase the net phase change rate ofthe liquid, and may include core inserts, which are more fully detailedin U.S. patent application Ser. No. 10/636,303 filed Aug. 7, 2003entitled “Method and Apparatus for Phase Change Enhancement,” thecontents of which are hereby incorporated by reference herein.

Scale control may be achieved using chemical treatments such as withpolyphosphates or polyaspartates, via plasma coating of appropriatecomponents through the use of galvanic or electrochemical processes, bytreatment with acids such as an organic acid, or through the use ofelectric and/or magnetic fields.

Other particular embodiments of the present invention may advantageouslyimprove energy efficiency of the overall system by including, forexample, highly efficient heat exchangers 400A and 400B as shown inFIGS. 19A and 19B, wherein such heat exchangers capitalize on availablesystemic and heat sources. In one particular embodiment, heat from atleast one of a plurality of sources passes through a multi-line heatexchanger 400A such as depicted in FIG. 19A, wherein a series oftwo-channel heat exchangers such as 38, 40, 42, and 44 are plumbed toproduce a multi-line effect. Note that in the particular multi-line heatexchanger embodiment shown in FIG. 19A, the flow of cold intake 39passes through all heat exchanger units 38, 40, 42, and 44; one heatsource, for example hot product 41, flows through heat exchanger units38 and 42; and another heat source, for example hot blowdown stream 43,flows through heat exchange units 40 and 44. In this way, multiple heatsources can be used to exchange with the cold intake flow 39.

Alternatively, a single multi-channel heat exchanger 400B such asdepicted in FIG. 19B may be used. In this particular embodiment, coldintake 39, and heat sources such as hot product 41 and hot blowdownstream 43, for example, flow through exchanger 400B simultaneously, butin opposite directions, thereby enabling heat exchange with cold intake39 from both heat sources 41 and 43 within a single heat exchanger 400B.Heat sources for heat exchanger 400 include product stream 41 andblowdown stream 43. Another possible heat source for the heat exchanger400 is radiative heat produced by steam pump drive motor 150, such as bythe motor windings, when the embodiment utilizes an external drivemotor. As discussed above, tube bundle heat exchanger technologydetailed in U.S. Pat. No. 4,520,868 may be utilized for the heatexchangers in accordance with the present invention, wherein elastomericend plates may be used to seal the tubes in a fixed orientation, inplace of metal or otherwise inelastic end plates soldered or brazed tothe heat exchanger tubes.

As discussed above with respect to FIGS. 1A and 1B, the power source 800may be, for example, an IC generator or a Stirling engine generator. Inone embodiment, the radiative heat produced by the generator may be usedto heat the intake stream, wherein the radiative heat produced by thegenerator is directed to heat exchanger 400. Such a heat exchanger wouldoptimally be positioned at the hot side of a three-channel heatexchanger, such as shown in FIG. 19B, where source liquid 39 entersevaporator 600. FIG. 14A or FIG. 4 (element 2506) also show such a heatexchanger that could be utilized with exhaust heat in one of thechannels.

If an external drive shaft motor is utilized, the overall system mayemploy an additional “cold” fluid pump of the gear-, diaphragm-, or“ram-”pump variety inline with cold intake line. In a particularembodiment, such a pump will be driven off the same rotor drive shaft asthe liquid ring pump. Other particular embodiments of the presentinvention may also be envisioned without a fluid intake pump, whereby agravity-feed mechanism or creation of a vacuum is used to drive thefluid through the system.

In another particular embodiment, sump 500 may employ a pre-heater orsupplemental heater, wherein a switch and temperature sensor with relaymonitor is employed to regulate heat input and temperature of the waterin the sump. Other fluid reservoirs may also contain temperaturesensors. For example, a temperature sensor in the sump could be used todetermine optimum conditions for the initiation of distillation as thestill heats up. Temperature sensors may also be employed to detectchanges in water temperature, thereby allowing adjustment of fluid flowrates to maintain overall still production.

In one embodiment, shown in FIG. 20, the evaporator and condenserpressures are measured, to assess overall system performance and/orprovide data to a control system. To avoid the use of expensive sensorsthat would be required to withstand the elevated temperatures ofcondenser/evaporator 600, pressure sensors P_(E) and P_(C) are mountedon fluid lines between the cold side of heat exchanger 400 andcorresponding control valves V_(F) and V_(C). To avoid measuring apressure less than the actual pressure of the system, which would occurwhen fluid is flowing for pressure sensors located at this position, thecontrol valve would be closed momentarily to stop flow. During the“no-flow” period, pressure will be constant from the control valve backto the evaporator or condenser, enabling accurate measurement of thesystem pressure. No adverse effects on still performance will occur fromthese short “no-flow” periods.

Still another embodiment of the present invention is designed toincrease the purity of the final purified liquid product byincorporating a filtering mechanism within intake 00, as shown in FIG.21A. A multi unit flip-filter 80, having a pivot joint 82 joining atleast two filter units 81 and 83, is situated within a filter housing80A which directs liquid through filter units 81 and 83 and facilitatesrotation of filter units 81 and 83 about central pivot joint 82. Asshown, blowdown stream 43 passes through flip-filter unit 81, whileintake liquid stream 39 simultaneously flows from intake 00 throughflip-filter unit 83 en route to purification. After some interval aflip-filter switch (not shown), rotates flip-filter 80 around itscentral axis, shown by the dotted line, at flip-filter pivot joint 82,such that filter unit 83, now fouled with contaminates filtered fromdirty intake liquid, is backwashed by blowdown stream 43, and filterunit 81 becomes the filter unit which filters intake liquid stream 39.In such an embodiment, o-ring gaskets 81A and 83A may be utilized asseals between filter units 81 and 83 and the liquid flow routes ofblow-down stream 43 and intake liquid stream 39, respectively.

In another embodiment, the multi-unit flip filter may be a multi-sectedcircular filter 80B, shown schematically in FIG. 21B. Multi unitflip-filter 80B, having a pivot point 82B about which multipleflip-filter units such as 81B and 83B pivot, may also be situated withinfilter housing 80C that directs liquid flow through individual filterunits 81B and 83B and facilitates rotation of filter 80B about pivotpoint 82B. As shown, blowdown stream 43 passing through one flip-filterunit 81B, while intake liquid stream 39 simultaneously flows from intake00 through flip-filter unit 83B en route to purification. As in FIG.21B, a flip-filter switch (not shown), rotates flip-filter 80B aroundits central axis, shown by the dotted line, at flip-filter pivot point82B, such that filter unit 83B, now fouled with contaminates filteredfrom dirty intake liquid, is backwashed by blowdown stream 43, andfilter unit 81B becomes the filter unit which filters intake liquidstream 39. A series of seals, as indicated by 81B-1 and 83B-1, areutilized between individual filter units 81B and 83B, to partitionblowdown stream 43 flowing through one filter section, from intakeliquid stream 39 flowing through another filter section.

Alternatively, a manual valve 85, such as shown schematically in FIG.22, could be employed to manually change the direction of water flow.Such a valve allows use of, for example, blowdown stream 43 tocontinuously clean one unit of each flip-filter, and with a singleoperation effectively switches which unit is being filtered and whichunit is being back-washed, thereby back-washing filter units 81 or 83without the need to actually flip filter 80 itself. As can be seen inFIG. 22, in one particular embodiment when valve 85 is in position A,filter unit 81 is filtering intake liquid 39, and filter unit 83 isbeing back-washed with blowdown stream 43. Upon switching valve 85 toposition B, filter unit 81 is now being backwashed by blowdown stream43, and filter unit 83 is now filtering input liquid 39.

In another particular embodiment, not shown, there may be an externalsystem including a holding tank with a pump for waste discharge, ifcircumstances require.

The particular embodiments described above generally operate aboveatmospheric pressure, typically around 10 psig. Such a systemadvantageously provides higher steam density at the higher pressure,thereby allowing more steam to be pumped through a positive displacementpump than at lower pressure. The resulting higher throughput providesoverall improved system efficiency. Further, the higher throughput andhigher system pressure reduces the power needed for compressor 100, andeliminates the need for two additional pumps—one for pumping condensedproduct 41 and another for pumping blowdown stream 43. Overallconstruction is simplified, as many shapes withstand internal pressurebetter than external pressure. Importantly, operating atsuper-atmospheric pressure reduces the impact of minor leaks on theoverall efficiency and performance. Non-condensable gases such as airinhibit the condensation process, and would be magnified atsub-atmospheric pressure, where minor leaks would serve to suck in air,something which will not occur in a system operating atsuper-atmospheric pressure.

When embodiments of the invention operate above atmospheric pressure,the use of a novel backpressure regulation may serve to control theoperating pressure of the system. FIGS. 23A and 23B depict views of abackpressure regulator consistent with an embodiment of the invention.The backpressure regulator 1100 has a vessel 1150 containing an orifice1110. One side of the orifice is connected to a pressurized conduit of asystem (e.g., the outlet of a compressor in a vapor compressiondistillation system) which may be exposed to the fluctuating elevatedpressure. The other side of the orifice terminates in a port 1170. Theport 1170 is covered by a movable stop 1130, in the shape of a ball. Thestop 1130 is retained to an arm 1120 by means of a retainer 1160 at afixed distance from a pivot pin 1140. The arm 1120 is attached by ahinge via the pivot pin 1140 to a point with a fixed relation to theorifice port 1170. The arm 1120 includes a counter mass 1180 suspendedfrom the arm that is movable along an axis 1190 such that the distancebetween the counter mass 1180 and the pivot pin 1140 may be varied. Inthe embodiment shown in FIG. 23A, the axial direction of the orifice1110 is perpendicular to the direction of the gravitational vector 1195.The backpressure regulator may also include a housing, which preventsforeign matter from entering the regulator and interfering with thefunction of the internal components.

In operating the embodiment shown in FIGS. 23A and 23B, the arm 1120maintains a horizontal position with respect to the direction of gravity1195 when the pressure in the pressurized conduit is below a given setpoint; this arm position, in this embodiment, is known as the closedposition, and corresponds to the stop 1130 covering the port 1170. Whenthe pressure in the conduit exceeds the set point, a force acts on thestop 1130, which results in a torque acting around the pivot pin 1140.The torque acts to rotate the arm 1120 around the pivot pin 1140 in acounter-clockwise direction, causing the arm to move away from itsclosed position and exposing the port 1170, which allows fluids toescape from the orifice 1110. When the pressure in the conduit isrelieved below the set point, the force of gas is no longer sufficientto keep the arm 1120 away from its closed position; thus, the arm 1120returns to the closed position, and the stop 1130 covers the port 1170.

In the embodiment of FIGS. 23A and 23B, the arm 1120 acts as a lever increating adjustable moments and serves to multiply the force applied bythe counter mass 1180 through the stop 1130 to the port 1170. This forcemultiplication reduces the weight needed to close the orifice 1110 asopposed to a design where the stop 1130 alone acts vertically on top ofthe orifice 1110, as in a pressure cooker. Thus a large port size, topromote expedited venting from a pressurized conduit, may be covered bya relatively lightweight, large-sized stop, the counter mass acting toadjust the desired set point; less design effort may be expended inchoosing specific port sizes and stop properties. The addition of anaxis 1190 for adjusting the position of the counter mass 1180, in thepresent embodiment, allows for changes in the multiplier ratio. As thecounter mass 1180 is moved to a position closer to the pivot pin 1140,the multiplier ratio is reduced, creating a lower closing force. If thecounter mass 1180 is moved farther from the pivot pin 1140, themultiplier ratio is increased, hence increasing the closing force.Therefore, the position of the counter mass 1180 effectively acts toadjust the set point of the backpressure regulator.

Adjustment of the backpressure regulator set point may be useful, whenthe backpressure regulator is utilized in systems at higher altitudes.When the atmospheric pressure is lower, the system operating pressure iscommensurately lower. As a result, the temperature of the distillationapparatus is lowered, which may adversely affect system performance. Aswell, such adjustment allows one to identify set points for thebackpressure regulator that are desired by the end user. The use of acounter mass to apply the closing force may also lower cost of thebackpressure regulator and reduce component fatigue. In a particularembodiment of the invention, the adjustable counter mass is designed toallow a range of set points with a lowest set point substantially lessthan or equal to 10 psig. and a highest set point substantially greaterthan or equal to 17 psig. Thus embodiments of the invention allow forprecise system pressure regulation, unlike devices which act simply assafety relief valves.

In another embodiment of the invention shown in FIGS. 24A and 24B, theorifice 1210 is configured such that the port 1270 is orientedvertically with respect to the direction of gravity 1295. Thus otherembodiments of the invention may accommodate any orifice orientationwhile maintaining the use of an adjustable counter mass.

In an embodiment of the invention shown in FIGS. 23A, 23B, and 25, thevessel 1150 includes a drain orifice 1115. Since the backpressureregulator 1100 may operate within a bounded region 1310 of a largesystem 1320, the drain orifice 1115 acts as a pathway to release fluidsthat are purged from the pressurized conduit 1340 through orifice 1110into the bounded region 1310. The drain orifice 1115 may connect thebounded region 1310 to another area of the larger system, or to theexternal environment 1330. In addition, the build-up of gases in thebounded region 1310 may result in condensation of such gases. Also,gases purged through the orifice 1110 may be entrained with droplets ofliquid that may accumulate in the bounded region 1310. Thus the drainorifice 1115 may also be used to purge any build up of condensables thataccumulate in the bounded region 1310; the condensables may also bereleased from the bounded region using a separate orifice 1350.

The backpressure regulator may be configured to allow a small leakagerate below the set point in order to purge the build up of volatilegases that act to insulate heat exchange and suppress boiling in asystem; the regulator is designed, however, to allow pressure to buildin the pressurized conduit despite this small leakage. In an embodimentof the invention, release of volatile components from a pressurizedconduit, below the set point of the backpressure regulator, may also beachieved through a specifically-designed leak vent while the arm of thebackpressure regulator is in the closed position. The leak vent isconfigured to allow a certain leakage rate from the port or the orificewhile the pressure in the conduit is below the set point. Such leak ventmay be designed by a variety of means known to those skilled in the art.Non-limiting examples include specific positioning of the stop and portto allow a small opening while the arm is in the closed position;designing the port such that a small opening, not coverable by the stop,is always exposed; specifying a particular rigid, non-compliant sealconfiguration between the stop and port when the arm is in the closedposition; and configuring the orifice leading to the port to have asmall opening to allow leakage of fluids.

In a particular embodiment of the invention directed toward the leakageof volatiles below the set point of the backpressure regulator, the port1410 has a small notch 1420 as shown in FIG. 26A and the close-up ofregion C of FIG. 26A depicted in FIG. 26B. Thus, when a stop is incontact with the port 1410, when the arm of the backpressure regulatoris in the closed position, a leak vent is present that allows a smallleakage through notch 1420. In another particular embodiment of theinvention, orifice 1510 has a small opening 1520, as depicted in FIG.27A and blow up of region E of FIG. 27A depicted in FIG. 27B. Theopening 1520 is configured such that a leak vent is present when thestop covers the port 1510 since fluids may leak through the opening1520.

Various features of a backpressure regulator consistent with embodimentsof the invention may be altered or modified. For example, stops to beused with backpressure regulators may have any shape, size, or massconsistent with desired operating conditions, such stops need not beball-shaped as shown in some embodiments of the invention discussedherein. As well, stops of different weight but similar sizes may beutilized with the retainer to alter the set point of the regulator.Similarly, counter masses of different sizes, shapes and masses may beutilized with embodiments of the invention as long as they areaccommodated by the axis and arm configurations (compare 1180 in FIGS.23A and 23B with 1280 in FIGS. 24A and 24B); such counter masses may beattached and oriented relative to the arm by any of a variety oftechniques apparent to those skilled in the art. The pivot pin placementneed not be positioned as shown in FIGS. 23 and 24, but may bepositioned wherever advantageous to provide the mechanical advantagerequired to achieve a particular pressure set point.

Embodiments of the invention may optionally utilize the drain orificefeature described earlier. Also, embodiments of the invention may notutilize the counter mass force adjustment feature, relying on thespecific properties of a stop to provide the set point for thebackpressure regulator.

Other embodiments of the invention may not utilize a vessel, but rely onorifices that are intrinsically part of the system. In such instances,the backpressure regulator arm may be directly attached to a portion ofthe system such that the arm, stop, and counter mass are appropriatelyoriented for the operation of the regulator.

As described above, various embodiments of this invention mayadvantageously provide a low-cost, easily maintained, highly efficient,portable, and failsafe liquid purification system that can provide areliable source of drinking water for use in all environments regardlessof initial water quality. The system of the present invention isintended to produce a continuous stream of portable water, for drinkingor medical applications, for example, on a personal or limited communityscale using a portable power source and moderate power budget. As anexample, at the desired efficiency ratio, it is envisioned that thepresent system may be utilized to produce approximately 10 gallons ofwater per hour on a power budget of approximately 500 watts. This may beachieved through a very efficient heat transfer process and a number ofsub-system design optimizations.

Knowledge of operating temperatures, TDS, and fluid flows providesinformation to allow production of portable water under a wide range ofambient temperatures, pressures, and dissolved solid content of thesource water. One particular embodiment may utilize a control methodwhereby such measurements (T, P, TDS, flow rates, etc) are used inconjunction with a simple algorithm and look-up table allowing anoperator or computer controller to set operating parameters for optimumperformance under existing ambient conditions.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodification as will be apparent to those skilled in the art. All suchvariations and modifications are intended to be within the scope of thepresent invention as defined in the specification.

1. A multi-line heat exchanger, the multi-line heat exchangercomprising: a) a first input for receiving a stream of a first fluid; b)a second input for receiving a stream of a second fluid; c) a thirdinput for receiving a stream of a third fluid; d) an interface fortransferring heat from the first and second fluids to the third fluid insuch a manner that all of the fluids are isolated from one another; e) afirst heat source stream from a first beat source coupled with theintake stream in a first sub-heat exchanger; f) a second heat sourcestream from a second heat source coupled with the intake stream from thefirst sub-heat exchanger in a second sub-heat exchanger; and g) at leasta third heat source stream, originating from the first heat source orfrom a third heat source, coupled with the intake stream from the secondheat sub-heat exchanger in at least a third sub-heat exchanger.